Batteries based on reversible circulation of lithium ions through an electrolyte containing a lithium salt are known. In this type of battery, the cathode comprises a current collector having a composite active material which generally comprises an active material allowing for the reversible insertion of lithium ions at high voltage, a binder, an electronically conductive agent and eventually an ionically conductive agent. The electrolyte is a solution of a lithium salt in a liquid solvent, a polymer solvent, or a polymer gel. And the anode comprises a lithium or lithium-based alloy film, or the anode comprises a current collector having an active material comprising a compound allowing for the reversible insertion of lithium ions at a voltage lower than the cathode, for example carbon, graphite, an oxide, or silicon.
The reversible insertion of lithium ions in the electrode material leads to a volume variation of the material. More specifically, a volume increase occurs during insertion of the ions and a volume decrease occurs during disinsertion of the ions. This volume variation has negative impacts on the battery. For example, volume variation may lead to the cracking of the passivation layer which is formed at the electrode surface during the first cycling, which may lead to a loss of capacity and/or electronic conductivity. These negative impacts can be assessed through studies based on scanning electron microscopy (SEM) in situ.
The extent of the volume variation depends on the material. For example, for two batteries different only in anode material, it is noted that volume variation of a carbon or graphite anode is relatively low, generally below 10%, which limits the cracking problems and resulting capacity loss. In contrast, volume variation for a silicon or silicon-based alloy anode is significantly higher, in the order of 300% for a silicon and lithium alloy. This is harmful to the battery. However, the maximum capacity allowed by a carbon anode is around 370 mAh/g, whereas the maximum capacity allowed by a Si—Li alloy anode is higher by a factor of 10. Accordingly, a Si—Li alloy anode allows for a good maximum capacity, but leads to a high volume variation of the material during cycling.
There is a need for an anode allowing for a good maximum capacity while leading to a low volume variation of the material during cycling.